The present disclosure relates to electronic circuits, systems and apparatuses, and in particular, to circuits and methods for controlling a boost switching regulator based on inductor current.
Switching regulators are a very efficient technique for providing and/or converting regulated voltages. Such regulators use one or more inductors and switches to store energy in magnetic fields generated as current flows through an inductor. Switches are used to selectively couple reference voltages to the inductor to either increase the energy in the inductor or allow the energy to flow to an output, for example. Accordingly, switching regulators are sometimes referred to as “switchers,” “converters” (e.g., a Boost Converter or Buck Switcher).
FIG. 1 shows an example boost switching regulator. In a boost switching regulator, the input voltage is typically less than the output voltage. Buck regulators, on the other hand, have input voltages greater than the output voltages. A variety of switching regulators exist that store energy in inductors and transfer the energy using switches. In this example, a constant (or direct current, “DC”) input voltage Vin is coupled to one terminal of an inductor L 101. The other terminal of the inductor 101 is coupled through a first switch 102 to a reference voltage (here, ground) and through a second switch 103 to an output terminal to produce a constant regulated output voltage Vout.
A boost switching regulator operates as follows. When switch 102 is closed (short circuited) and switch 103 is open (open circuited), the second terminal of inductor 101 is coupled to ground and a positive voltage Vout is applied across the terminals of inductor 101. Accordingly, during this first phase, denoted φ1, current in the inductor, IL, increases and energy is stored in the inductor. When switch 102 is opened and switch 103 is closed, the instantaneous inductor current remains unchanged, and such inductor current flows to the output terminal and into a load, which is represented here as a resistor Ro. During this second phase, denoted Φ2, the voltage across the inductor reverses polarity because Vout is larger than Vin in a boost converter. Accordingly, inductor current IL decreases during this phase of operation. Switches 102 and 103 may turn on and off over a particular time period, or cycle, to alternately charge and discharge the energy in the inductor. In some applications, the time switch 103 is on (closed) and switch 102 is off (open) may cause the inductor current IL flowing from inductor 101 through switch 103 to ramp down from a positive value to a lower positive value before the end of a switching cycle. In some applications the cycle and reverse voltage (Vout-Vin) may cause the inductor current IL and the current flowing through switch 103 to change polarity and go from positive (i.e., flowing to the output) to negative (flowing from the output to the input), such as in a forced continuous conduction mode (CCM) operation where the regulator may sink current, for example.
The regulated output voltage Vout is controlled by a feedback loop implemented using control circuitry 104. In this example, control circuit 104 senses the output voltage Vout and inductor current IL to regulate the output voltage Vout by controlling the time switches 102 and 103 are turned on and off during each cycle.
One problem associated with switching regulators pertains to controlling the system using current (referred to as current control) at very low duty cycles. For example, maintaining well-regulated current mode PWM control with very small duty cycles (e.g., 2%) can be very challenging. In some applications, forced CCM may be required to maintain a low ripple and negative current. Accordingly, as mentioned above, a boost switching regulator may have an inductor current that changes polarity during a switching cycle. Such changes in polarity cause problems for control circuits attempting to implement a current control scheme.